Session State

I have a multipage shopping cart application. On page one the shopper selects an item and quantity, then click a button to add item to cart. On cart page are buttons to return to add more items or to checkout. When the user chooses to checkout I show a page to collect first & last name. I then want to allow the user to continue shopping. When the user chooses to checkout the next time I want to have the name info entered previously. I understnd how to check if the session item is null for the first pass. I build try to retrieve the sesion data with commands below.

Session["FName"] = FName.Text; - move item to session

FName.Text = (string)(Session["FName"]); - get item from session

Have not been able to see data when returning from select item page of project...I am trying, but a bit confused in using prerender and that may be part of the problem....